Why Does My Shower Go Cold When I Turn Another Tap On?

Dennis Howard
by Dennis Howard

We have all experienced it at least once. You are enjoying a nice warm shower, and, without warning, the shower turns icy cold. It is an unpleasant experience, at best. Why does the shower go cold when someone turns on another tap in the house?

Your shower goes cold when you turn another tap on due to the sudden reduction in your water’s flow, causing a temperature drop. Since there is less water flowing into your water heater, it causes a drop in temperature at the showerhead. This drop only lasts a few seconds before returning to normal.

A reduction in flow is the most seen reason for temperature changes in the shower when someone opens a tap or flushes a toilet. However, other things can be the culprit. Once you determine the cause for the temperature change in your water flow, several remedies may help with your water temperature problem.

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Understanding Water Flow and Home Plumbing

The first thing to understand about the water supply lines in your home is that the builder is in business to make money. That means that keeping costs as low as possible is expected. When putting in the pipes, the plumber wants to use the least amount of material to get the job done.

Most homes have a single line that supplies all the faucets and other outlets. Smaller diameter lines run from the main supply line to the point of use. The more faucets that are open, the less water flow is available for other uses. That equates to temperature fluctuations when you are in the shower.

Do I Need to Have my House Replumbed?

Replumbing your entire home to mitigate problems with temperature is not a viable option for most of us. The cost can be prohibitive, especially if your home sits on a concrete slab costs can grow even larger. Replumbing a house is a job for a professional plumber who knows the local building codes and requirements.

Options To Keep Shower Warm

There are several options on the market to help even out the temperature fluctuations that you may experience in your home. These options range from the simple to the extreme. Finding the right balance for your home is the key.

Reduce Water Flow to Your Toilets

Toilets are often the worst problem with temperature fluctuations. Toilets require only a cold water connection to operate. When the toilet is flushed, it demands cold water to refill the toilet tank. This flow demand at the toilet robs the water heater of flow and can reduce the flow of hot water to the shower. You get that sudden unpleasant drop in temperature in your shower.

Use the Supply Valve

Closing the supply valve at the toilet may solve your temperature fluctuation problem. Reducing the water flow to the toilet can have negative side effects such as:

  • The toilet will take longer to refill the tank
  • The refilling process may be noisier
  • You may still have some temperature fluctuations in your shower

Reduce the Amount of Water Your Toilet Uses

Many people have used this trick for years to reduce the amount of water a toilet uses for each flush. You can put a brick, a small filled water bottle, or something else that will reduce the amount of water your toilet tank holds.

This method won’t address the water flow issues but will reduce the time it takes for the toilet tank to refill. Shortening the refill time reduces the effect at your water heater and lessens the impact at your shower.

Like reducing the water flow to the toilet, reducing the amount of water in the tank can have negative effects. The most pronounced may be difficulty removing solids from the toilet bowl due to the lower amount of water available for each flush.

Smarter Mixing at the Shower

If your shower hash an older shower controls don’t have thermostatic mixing. Installing a new shower valve assembly may be the best way to fix your cold shower problem. Older shower mixers are simple valves that open the hot and cold water lines to mix the water. The flow rate from each pipe determines the ratio of hot to cold water.

New thermostatic controls are much smarter. These smart valves sense changes in flow rates from both the hot and cold supply lines. When a tap opens or a toilet flushes, the valve senses the flow change. The valve then balances the flow to keep the ratio of hold and cold the same ending temperature reductions.

Relacing a mixing valve on a shower is a project that some DIY’ers can undertake. However, in most instances, the services of a licensed plumber is a better option. Replacing a mixing valve may also require tile work if there is no access to the plumbing.

Adding an Expansion Tank to the Water Heater

Adding an expansion tank to your water heater system may help solve your temperature fluctuations. An expansion tank adds capacity to your hot water system that can even out the temperature fluctuations. Expansion tank additions to an existing hot water system are relatively reasonable.

Shower Replumbing

Replumbing a home can be a large and expensive project. The cost can depend on the size of your house, the type of construction, and the type of replumbing you chose. The services of a qualified and licensed plumber are essential for these types of projects.

Increasing the Flow Rate by Enlarging the Pipes

If your home has a trunk and branch supply system, you may need to increase the size of the pipes. Running new pipes, in many cases, requires removing the old pipes before installing new pipes. With the old pipes removed, the plumber will install the new pipes and make the connections.

If your home is on a pier and beam foundation or sits over a basement, this project is easier to accomplish. A concrete slab foundation often means that the pipes must run through an attic space. In cold climates, this may not be an option due to the chance of freezing. A licensed plumber is your best source of information in this case.

A Manifold System – Redesigning the Entire System

Your plumber may suggest replacing your trunk and branch system of supply with a manifold system. If it is economically feasible, this is a more efficient design that is often better. A manifold system has several advantages.

  • The manifold system uses a central supply manifold to balance the water supply sent to each faucet or point of use. The manifold system reduces fluctuations in the water flow.
  • Having a central manifold allows better control of water flow throughout the house. Each distribution line can be adjusted to fine-tune the water flow.

Installing a manifold system is probably the most radical and expensive of the solutions. Planning the installation of a manifold system is not a project for a homeowner. The knowledge and training of a plumber will ensure that the system is balanced and tuned.

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Addressing that Cold-Shower Syndrome

If you suffer from the cold-shower syndrome, the problem is unbalanced water flow in your plumbing system. Often, the easiest fix is to find the source of the water flow problem and correct the problem there. The solutions can be as simple as reducing the flow to the toilet or as complicated as a replumbing job. It is up to you to decide which solution best fits your situation.

We hope that is article answers some of your questions about your home water supply and the problems with temperature fluctuations.

Dennis Howard
Dennis Howard

Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.

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